Our first aim is to develop an Early Mathematics Assessment System (EMAS) appropriate for young children (3- to 5-year olds) that will serve three major functions. The long form (L-EMAS) can be used to (1) evaluate the effectiveness of a variety of curricula, (2) and to provide immediate and specific cognitive process information that can be used to guide instruction. (3) The short form (S-EMAS) can be used as a screening instrument for identifying children at risk for mathematical difficulties and those who might require comprehensive assessment and intervention. The EMAS will have several key features. It will measure a broad range of mathematical content, assessing number, operations, shape, space, measurement and pattern. It also will measure a broad range of mathematical proficiency, including performance;cognitive processes underlying performance;comprehension and use of mathematical language;and children's "motivation"-attentiveness and affect. The EMAS will be research-based, drawing on modern cognitive science, developmental and educational research. It will engage and motivate young children through the use of games or purposeful activities such as a birthday party. This type of context should ensure that the EMAS, which will be translated into Spanish, can be used with a diverse population. Our second aim is to develop innovative technology whereby a personal digital assistant (PDA) will guide assessors in administering the EMAS. The technology will help them to use flexible probes modeled on the clinical interview to gain greater insight into student proficiency. Our third aim is to use statistical procedures to ensure that the EMAS is reliable and valid. The psychometric properties of both the EMAS will be investigated using both classical test theory (CTT) and item response theory (IRT) approaches to ensure high reliability and validity of the scale and quality of the items. We will conduct reliability studies and will use IRT to provide item and test information. We will also conduct validation studies. Once their reliability and validity have been shown to be strong, the L-EMAS and S-EMAS will be ready for norming. Our fourth aim is to help assessors to use the EMAS and to investigate their use of it. We will design and evaluate professional developmental activities to enable early childhood professionals to use the PDA comfortably to administer the EMAS and to interpret the results. We will also investigate how assessors use the EMAS and learn from it. The EMAS will contribute to the evaluation and improvement of mathematics education for young children.